In order to grind the surface of a workpiece with high-precision surface roughness a grinding machine is provided with two grinding wheel heads, on one of which a grinding wheel for rough grinding is rotatably supported, and on the other of which a grinding wheel for finish grinding is rotatably supported. The grinding machine rough-grinds the workpiece with high grinding efficiency with using the grinding wheel for rough grinding and then finish-grinds the rough-ground workpiece with high-precision surface roughness with using the grinding wheel for finish grinding. It is done that after the rough grinding with using the grinding wheel, the workpiece is lapped for high-precision surface roughness with using a lapping tape.
Further, in the centerless roll grinding machine disclosed in Japanese Unexamined Patent Publication No. 1999-104940, a wide combined grinding wheel having a grinding wheel for rough grinding 11a, a grinding wheel for medium finish grinding 11b, and a grinding wheel for finish grinding 11c is used as a grinding wheel 11. Further, while a roll 2, which is supported and rotated on an adjustment wheel 13, and a knife blade 14 to pass between the grinding wheel 11 and the adjustment wheel 13, the rough grinding, the medium finish grinding, and the finish grinding are conducted in one pass.
However, in the above-mentioned conventional grinding machine, as the workpiece is rough-ground by the grinding wheel for rough grinding, and thereafter finish-ground or lapped by the grinding wheel for finish grinding or by the lapping tape, it takes time to move the workpiece from a position opposite the grinding wheel for rough grinding to a position opposite the grinding wheel for finish grinding or a position opposite the lapping tape, so that the time required to perform grinding increases. Further, there is a problem that the grinding machine is expensive.
In the centerless grinding machine disclosed in Japanese Unexamined Patent Publication No. 1999-104940, when depth of cut of the grinding wheel is ultraminute, the roll 2 is not fed in an axial direction. Hence, a roll surface cannot be ground with superhigh-precision surface roughness.
Accordingly, it is a primary object of the present invention to resolve the above mentioned problem and to provide a grinding wheel capable of rough-grinding the surface of a workpiece and finish-grinding it with superhigh-precision surface roughness with using one grinding wheel.